1. Field of the Invention
The present invention relates to a rotating body tracing control apparatus which performs a tracing operation while rotating a model and a workpiece, and more particularly, to a rotating body tracing control apparatus in which a method of setting a potential line for defining a tracing range is improved.
2. Description of the Related Art
A rotating body tracing control apparatus is used when machining, for example, a cylindrical cam, and in such a rotating body tracing control apparatus, a model and a workpiece are rotated at the same angular speed as the speed at which the surface of the model is traced by a tracer head, and the feeding speed with respect to the Z-axis direction is obtained in accordance with a detection signal, whereby the movement of the tracer head and a cutter head is controlled.
FIG. 3 is a diagram showing the relationship between a stylus and a cylindrical cam model which is traced by using the rotating body tracing control apparatus.
In FIG. 3 the stylus 5 at the distal end of the tracer head, which is movable in the Z-axis direction, detects the distance between the central axis of rotation (X-axis) of the model 6 and the point of contact of the stylus 5 with the model, by determining the displacement of the stylus 5. The tracing direction of the tracer head corresponds to the X-axis direction, and a pick feed direction to an A-axis direction.
Software limit switches, such as indicated by broken lines LXN and LXP, can be set by assigning points XN and XP on a line extending in the tracing direction (X-axis direction), and a tracing region is decided by using these software limit switches.
Accordingly, the tracer head executes a tracing with respect to the X-axis direction, and the movement thereof is stopped in the X-axis direction when the contact point of the stylus 5 comes into contact with the software limit switches LXN and LXP. Thereafter, pick feed is effected in the A-axis direction, and the X-axis is traced in the opposite direction. These operation processes are repeatedly executed.
When tracing the model 6, such as a cylindrical cam, having a groove which is curved along the X-axis direction, the tracer head is expected only to trace the groove portion of the cylindrical cam, and does not trace the outer peripheral surface of the model 6, such as regions F1 and F2.
Conventionally, however, one point on the central axis (X-axis in FIG. 3) of rotation is assigned to set the software limit switches, so that the software limit switches must be inevitably set by assigning the points XN and XP even when tracing the cylindrical cam model 6. Therefore, when tracing a cylindrical cam like the model 6, the tracer head traces the whole region of the peripheral surface of the cylinder, including the points XN and XP, and thus, conventionally, the region to be traced is so extensive that the tracing work requires much time.